[TowerTalk] bracketed 45G
W2RU - Bud Hippisley
W2RU at frontiernet.net
Thu Jun 15 22:05:25 EDT 2006
Jim Jarvis wrote:
> fwd'd to reflector, because it's a relevant question:
> N2EA wrote:
>> If your structure has deep eaves, you'll be
>> stuck with using the Rohn house bracket. I found that to be more
>> flexible than I wished, which drove me to design my own.
> Bud, W2RU, wrote:
> Gee, I wonder if you're thinking of the "older" Rohn brackets? Compared
> to the Rohn house brackets I bought a few decades ago for my Rohn 25
> towers, the Rohn house brackets I bought six years ago for my Rohn 45
> tower are *massive* and about as flexible as a cinder block.
> N2EA replied:
> Bud...I dunno. May well be. The ones I saw only
> intersected two joists, not 3, and they extended out
> from the building by 22". I wanted more tie-in to
> the structure.
My Rohn brackets are five feet across, and have five nut-and-bolt
assemblies tying each of them to a rather substantial backer plate
system in my garage and attic walls. (I had the advantage of having
them on-site and ready to go for my contractor to install when my
addition was put on six years ago.) The arms extend 38 inches from the
wall, which should cover most eave extensions. In my case I have only a
one foot overhang on my gable end, so I have the entire tower footprint
totally nestled within the footprint of the two arms.
> My personal problem was lack of access to
> the roof and floor joists-- I had to lag-screw into them,
> rather than using backing plates.
Yes, my Rohn 25 brackets at my previous homes were done that way.
> For the chap who originally asked, however, I believe he's still
> constrained by the available engineering data and code compliance
By all means. However:
> Gotta use the mfr's data.
Unfortunately, the manufacturer doesn't provide many useful data points
of "height above upper bracket" versus antenna wind load. For
instance, I have a Cushcraft A-3 tribander and a T2X on top of my
house-bracketed tower, not 25.9 square feet of antenna. For
house-bracketed towers, I suspect the former is more typical than the
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